Ultrafast magnetization reversal in ferromagnetic spin valves: An s-d model perspective

We present an extension to simple s -d models, aiming at simulating ultrafast magnetization dynamics and spin transport in metallic heterostructures. In particular, we consider an alternative spin dissipation channel due to a finite exchange splitting of the s band. From this theory, we show three different mechanisms governing the dynamics of spin accumulation. On top of the already widely discussed "-dM/dt" electron-magnon mechanism, we study the role of a dynamic change of exchange splitting (of conduction electrons) as well as the rotation of spins reflected at an interface with a ferromagnet. Finally, we use the presented theory to explain the recent observation of subpicosecond reversal of a ferromagnet in rare-earth free spin valves. Our conclusion agrees with the one of J. Igarashi et al. [Nat. Mater. (2023)] favoring magnetization reversal due to the rotation of the spin polarization of a reflected spin current.